Blood Pressure Variability: Why Blood Pressure Is Not Simply “High or Low” – What Studies Show About Blood Pressure Fluctuations
Many people with high blood pressure are familiar with this situation: at the doctor's office, their blood pressure is sometimes higher and sometimes lower. At home, too, the readings vary from one measurement to the next. For a long time, this was considered normal and unimportant – only the average blood pressure was thought to matter.
However, research shows that how much blood pressure fluctuates can be just as important as the average itself. Large studies have investigated whether fluctuations in blood pressure – known as blood pressure variability – affect the risk of cardiovascular disease.
For this reason, Tensana displays the blood pressure variability metrics listed below for Premium members from version 8.3.0 onward.
What is blood pressure variability?
Blood pressure changes constantly – from one heartbeat to the next, throughout the day, from day to day, or from one doctor's visit to the next. These fluctuations are known as blood pressure variability. A distinction is made between:
- Short-term fluctuations – over minutes or hours (e.g. on a 24-hour monitor)
- Medium-term fluctuations – over days or weeks (e.g. when taking measurements at home)
- Long-term fluctuations – over months or years (e.g. between doctor's appointments)
Researchers wanted to know: Do people with greater fluctuations have a higher risk of heart attack, stroke, or death?
The most important studies
1. 2016 BMJ study (Oxford research team)
This large meta-analysis summarized over 40 studies involving tens of thousands of people.
Result:
- Greater blood pressure variability was associated with a significantly higher risk of cardiovascular disease (e.g. heart attack, stroke).
- Mortality (overall and cardiovascular) was also higher.
The association persisted after taking average blood pressure into account. This means that the risk is influenced not only by how high the blood pressure is, but also by how stable it remains.
2. JAMA Network Open study (USA, 2021)
The study examined older people with high blood pressure and coronary heart disease.
Result:
- Those who had greater fluctuations in blood pressure between doctor visits over the course of a year were more likely to die in subsequent years – despite having a similar average reading.
- The effect was stronger in women than in men.
Significance: High variability may be more dangerous in the long term, especially in older female patients.
3. Review by Parati et al. (Journal of Hypertension, 2005)
Review of the causes and measurement of blood pressure variability:
- People with high blood pressure often show greater fluctuations.
- Regardless of the average value, fluctuations can contribute to damage to the heart, kidneys, and blood vessels.
- Long-acting medications that work consistently over 24 hours can reduce fluctuations.
Conclusion: Pay attention not only to "the single reading," but also to the pattern over time.
4. Specialist book: Blood Pressure and Arterial Wall Mechanics in Cardiovascular Diseases
Physical principles: Stiffer blood vessels (e.g. due to aging or atherosclerosis) are more sensitive to changes in pressure – fluctuations increase. The interplay between vascular elasticity and variability influences the risk of cardiovascular disease.
How blood pressure variability is measured – the key metrics
Researchers use various measures to describe how much blood pressure fluctuates. Here are four important terms:
1. Standard deviation (SD – Standard Deviation)
Meaning: The SD shows how far the measurements are from the average. The larger it is, the greater the variation.
Example:
- Average: 130 mmHg
- Measurements: 128–132 → SD = 2 mmHg (stable)
- Measurements: 120–140 → SD = 10 mmHg (unstable)
Reference values: SD < 6 mmHg = stable ˇ 6–12 mmHg = moderate ˇ > 12 mmHg = highly variable
2. Coefficient of Variation (CV – Coefficient of Variation)
Meaning: Relates the variation to the average.
Formula: CV = (SD / mean) × 100 %
Example:
- Person A: Mean = 100 mmHg, SD = 10 → CV = 10%
- Person B: Mean = 150 mmHg, SD = 10 → CV ≈ 6.7%
Reference values: CV < 8% = stable ˇ 8–12% = moderate ˇ > 12% = highly variable
3. Average Real Variability (ARV)
Meaning: Measures how much blood pressure changes from one measurement to the next; the order is taken into account.
Example:
- 120 → 125 → 130 → 135 mmHg → ARV = 5 mmHg (stable)
- 120 → 140 → 115 → 135 mmHg → ARV ≈ 22 mmHg (highly variable)
Reference values: ARV < 7 mmHg = stable ˇ 7–12 mmHg = moderate ˇ > 12 mmHg = high
4. Variability Independent of the Mean (VIM)
Meaning: Corrects for the effect of higher mean values on the degree of variability, thereby showing the “true” instability.
- High VIM = unstable blood pressure, even with a normal mean.
- Low VIM = stable values, regardless of the level.
Assessment: No fixed thresholds; the lower the value, the more stable it is.
Quick overview – what the numbers mean
| Measure | Description | Typical values | A high number means … |
|---|---|---|---|
| SD | Spread of all values around the average | < 6 = stable ˇ 6–12 = moderate ˇ > 12 = unstable | Blood pressure fluctuates considerably |
| CV | Variation relative to the average (in %) | < 8 % = stable ˇ 8–12 % = moderate ˇ > 12 % = unstable | Large relative variation |
| ARV | Average difference between consecutive measurements | < 7 = stable ˇ 7–12 = moderate ˇ > 12 = unstable | Blood pressure “jumps” considerably |
| VIM | Variation independent of the average | no fixed values | “True” instability, independent of the mean |
Minimum requirements for calculating these values
For metrics such as SD, CV, ARV or VIM to be reliable, they require sufficient, high-quality measurement data. One or two measurements reveal little – they could be due to chance.
1. Number of measurements
| Type of measurement | Recommended minimum number | Why this is important |
|---|---|---|
| 24-hour measurement (ambulatory) | At least 40–50 valid individual readings (day + night) | Only then can typical day-night fluctuations be identified |
| Home measurement (at home) | At least 2 measurements/day for 7 days → approx. 14 measurements or more | Provides a realistic picture of daily fluctuations |
| Long-term monitoring (doctor's visits) | At least 3–4 appointments over several months | This is the only way to identify long-term trends and variability |
The more measurements there are, the more accurate and meaningful the values are. With fewer than 10 measurements, SD, CV, ARV, and VIM are not reliable.
2. Time intervals between measurements
- Distribute measurements as evenly as possible over time.
- For 24-hour measurements: every 20–30 minutes during the day and approximately every hour at night.
- For measurements at home, take them at the same time whenever possible (e.g. in the morning and evening).
- Long gaps distort the result.
3. Measurement quality
- Whenever possible, use the same blood pressure monitor.
- Sit quietly for 5 minutes before taking the measurement.
- Avoid coffee, physical activity, and stress immediately beforehand.
- Exclude measurement errors/outliers (e.g. due to incorrect cuff placement).
4. Specific minimum requirements for each metric
| Metric | For a reliable calculation, you need … |
|---|---|
| SD (standard deviation) | At least 10–15 measurements under similar conditions |
| CV (coefficient of variation) | As for SD, plus the mean of the same data |
| ARV (Average Real Variability) | At least 3–4 consecutive measurements, preferably > 10 |
| VIM (Variability Independent of Mean) | Larger data set, e.g. several days/weeks, ideally > 20 measurements |
Simply put
- Individual measurements are not sufficient.
- At least one week of home measurements or a 24-hour measurement is needed to calculate reliable variability values.
- Regularity and consistent conditions are more important than the sheer number of measurements.
Practical example
With measurements taken in the morning and evening for one week (≈ 14 measurements), SD, CV, and ARV can be calculated reliably. An additional 24-hour measurement or measurements taken over several weeks also make it possible to determine VIM – providing a comprehensive picture of blood pressure stability.
Conclusion
Research clearly shows that not only how high blood pressure is, but also how stable it is, can determine health and lifespan.
- Measure regularly
- Take fluctuations seriously
- Discuss with your doctor how they can be reduced
Stable blood pressure protects the heart, brain, and blood vessels – and is an important step toward a healthier life. To make blood pressure fluctuations easy to identify, they can be displayed for Premium members in the Tensana app from app version 8.3.0 onward.
Sources and further reading
- Stevens, S. L., Wood, S., Koshiaris, C., et al. (2016). Blood pressure variability and cardiovascular disease: Systematic review and meta-analysis. The BMJ, 354, i4098. bmj.com
- Li, J., Zhao, D., Wei, X., et al. (2021). Association of 1-Year Blood Pressure Variability With Long-Term Mortality in Older Patients With Hypertension and Coronary Artery Disease. JAMA Network Open, 4(4), e219301. jamanetwork.com
- Parati, G., Pomidossi, G., Albini, F., Malaspina, D., & Mancia, G. (2005). Blood pressure variability: Its measurement and significance in hypertension. Journal of Hypertension, 23(Suppl. 1), S19–S25. journals.lww.com
- O’Rourke, M. F., & Hashimoto, J. (2013). Blood Pressure and Arterial Wall Mechanics in Cardiovascular Diseases. London: Springer. springer.com
- German Hypertension League (DHL) / German Society for Hypertension and Prevention. Guidelines on blood pressure measurement and self-monitoring, 2023. hochdruckliga.de
- European Society of Hypertension (ESH). (2023). ESH Guidelines for the management of arterial hypertension. Journal of Hypertension, 41(6), 1873–2081.
Author Sabine Croci is a qualified medical assistant with many years of experience in internal medicine and cardiology practices as well as outpatient care, and has headed the specialist editorial team at Tensana since 2015. Thanks to her extensive additional qualifications as an emergency medical technician, first responder, and in various areas of therapy and emergency care, she provides well-founded, practical, and reliably verified information.
